CN113078679A

CN113078679A - Multi-parallel inverter circuit grid-connected system and control method

Info

Publication number: CN113078679A
Application number: CN202110415647.0A
Authority: CN
Inventors: 李俊杰; 辛凯; 于心宇
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Digital Power Technologies Co Ltd
Priority date: 2021-04-16
Filing date: 2021-04-16
Publication date: 2021-07-06
Anticipated expiration: 2041-04-16
Also published as: CN113078679B

Abstract

The grid-connected system comprises a controller and at least two inverter circuits, wherein the output ends of the at least two inverter circuits are connected in parallel, when the at least two inverters are required to be controlled to output a certain current in parallel, the controller can control the output current of each inverter circuit in the grid-connected system according to the junction temperature of at least one switching device of each inverter circuit in the grid-connected system, so that the difference value between the junction temperature of at least one switching device of any one inverter circuit in the at least two inverter circuits and the junction temperature of at least one switching device of any one inverter circuit in the at least two inverter circuits is smaller than or equal to a difference threshold value; the current is flexibly distributed based on the junction temperature of the switching device, the heat loss balance control of each inverter circuit in the grid-connected system can be realized, the service life of the inverter circuit is ensured, and the active maximum capacity output of the grid-connected system can be realized.

Description

Multi-parallel inverter circuit grid-connected system and control method

Technical Field

The embodiment of the invention relates to the field of power systems, in particular to a multi-parallel inverter circuit grid-connected system and a control method.

Background

The inverter circuit is an interface circuit of new energy grid connection, and along with the increase of the capacity of a new energy power station, the number of inverter circuits which are operated in parallel is greatly increased, and the complexity of the system is increased. In a grid-connected system of multiple parallel inverter circuits, the technical problem of maximally transmitting active power and protecting the service life of the inverter circuits is worth researching.

Disclosure of Invention

The application provides a grid-connected system of multiple parallel inverter circuits and a control method, which can realize the heat loss balance control of each inverter circuit in the grid-connected system, ensure the service life of the inverter circuits and realize the active maximum capacity output of the grid-connected system.

The embodiment of the application provides a grid-connected system with multiple parallel inverter circuits, which comprises a controller and at least two inverter circuits, wherein the at least two inverter circuits comprise input ends and output ends, the output ends of the at least two inverter circuits are connected in parallel, the input ends of the at least two inverter circuits are respectively connected with a direct current input, and each inverter circuit comprises at least one switching device.

In the grid-connected system of multiple parallel inverter circuits according to the embodiment of the present invention, when it is necessary to control at least two inverters to output a certain current in parallel, the controller may control the output current of each of the at least two inverter circuits in the grid-connected system according to the junction temperature of at least one switching device of each of the at least two inverter circuits in the grid-connected system, so that the difference between the junction temperature of at least one switching device of any one of the at least two inverter circuits and the junction temperature of at least one switching device of any one of the at least two inverter circuits is less than or equal to the difference threshold; the sum of all the output currents is the total current which needs to be output by at least two inverter circuits, namely the total scheduling current. The current is flexibly distributed based on the junction temperature of the switching device, the heat loss balance control of each inverter circuit in the grid-connected system can be realized, the service life of the inverter circuit is ensured, and the active maximum capacity output of the grid-connected system can be realized.

In one possible embodiment, the controller is further configured to determine a junction temperature of at least one switching device of each of the at least two inverter circuits; or the inverter circuit is used for determining the junction temperature of at least one switching device of the inverter circuit and sending the junction temperature to the controller.

In the embodiment of the invention, the junction temperature of the switching device of each inverter circuit in the grid-connected system can be determined, and then the junction temperature of the switching device is transmitted to the controller for processing, so that the heat loss balance control of each inverter circuit in the grid-connected system is realized based on a master-slave control framework. The junction temperature of the switching device of each inverter circuit in the grid-connected system can be determined by the controller, and then the heat loss balance control of the inverter circuits is realized according to the junction temperature of the switching devices, so that the links of data transmission are reduced, and the accuracy of junction temperature data is ensured.

In one possible embodiment, the controller or the inverter circuit is specifically configured to, in determining the junction temperature of the switching device of the inverter circuit: and determining the junction temperature of a switching device of the inverter circuit at the t +1 moment according to the operation parameters and the parameters of the switching device of the inverter circuit at the t moment, wherein the parameters of the switching device are the characteristic parameters of the switching device in the inverter circuit. The operation parameters comprise at least one of active current, reactive current, apparent current, direct current bus voltage, thermal resistance coefficient of the inverter circuit, switching frequency of a switching device of the inverter circuit, modulation wave and detection temperature.

In the embodiment of the invention, the junction temperature of the switching device of the inverter circuit at the t +1 moment is predicted according to the operation parameter of the inverter circuit at the t moment and the parameter of the switching device, so that the balance of heat loss of the inverter circuit is further controlled according to the junction temperature of the switching device.

In one possible embodiment, the controller is specifically configured to, in controlling the output current of each of the at least two inverter circuits: controlling each of the at least two inverter circuits to output a first current according to the junction temperature of the switching device of each of the at least two inverter circuits, the preset maximum junction temperature and the total scheduled current of the system, wherein for each of the at least two inverter circuits, the first current of the inverter circuit is less than or equal to the maximum working current of the inverter circuit; the junction temperature of the switching device of the inverter circuit is the junction temperature of any one of the at least one switching device of the inverter circuit or the junction temperature of the switching device of which the junction temperature meets the preset condition.

In the embodiment of the invention, the total scheduled current of the system is the total current output by at least two inverter circuits in the grid-connected system, the total scheduled current information may be carried in a current scheduling command, which the controller, after receiving, the controller controls each inverter circuit of the at least two inverter circuits to output a first current according to the junction temperature of the switching device, the preset maximum junction temperature and the total scheduling current of each inverter circuit of the at least two inverter circuits, the first current which is required to be output by each inverter circuit in the grid-connected system is distributed to each inverter circuit, so that the first current output by each inverter circuit does not exceed the maximum working current of each inverter circuit, the active power generation loss caused by maximum capacity limitation and heat derating is reduced, the active maximum capacity output of the grid-connected system can be realized, the heat loss balance of each inverter circuit can be realized, and the service life loss of the inverter circuits caused by heavy load or overheating is reduced.

In a possible embodiment, when the total scheduled current is a total scheduled reactive current or a total scheduled active current, the controller is specifically configured to, in determining the first current of each of the at least two inverter circuits: determining a current distribution coefficient of each inverter circuit in the N inverter circuits according to the junction temperature of a switching device of each inverter circuit in the N inverter circuits and the preset maximum junction temperature, wherein N is more than or equal to 2; according to the current distribution coefficient and the total scheduling current I of each inverter circuit₁Determining a first current for each inverter circuit; determining that N first inversions exist in the N inverter circuits, wherein the first current of the inverter circuit is larger than the maximum working current of the inverter circuitWhen the circuit is changed, if n is an integer, setting the first current of each first inverter circuit in the n first inverter circuits as the first maximum working current of the first inverter circuit; let N be N-N, I₁＝I₁A, a is the sum of the first maximum working currents of the N first inverter circuits, and the above steps are repeatedly performed until each inverter circuit in the N inverter circuits has a first current less than or equal to the first maximum working current of the inverter circuit.

In the embodiment of the invention, when the current scheduling instruction is a reactive current scheduling instruction or an active current scheduling instruction, correspondingly, the reactive current scheduling instruction carries total scheduling reactive current information, and the total scheduling current at the moment is the total scheduling reactive current; the active current scheduling instruction carries total scheduling active current information, and the total scheduling current at the moment is the total scheduling active current. In addition, when the controller determines the first current of each inverter circuit, the controller first determines the current distribution coefficient of each inverter circuit in the N inverter circuits according to the junction temperature of the switching device of the N inverter circuits and the preset maximum junction temperature, so as to determine the total scheduling current I according to the current distribution coefficient₁Determining a first current for each inverter circuit; then, when it is determined that N first inverter circuits with the first current of the inverter circuit larger than the maximum working current of the inverter circuit exist in the N inverter circuits, setting the first current of the N first inverter circuits as the first maximum working current of the corresponding inverter circuit, redistributing the residual total scheduled current (namely the residual current after subtracting the current distributed by the N first inverter circuits from the total scheduled current) to the inverter circuits except the N first inverter circuits in the N inverter circuits, and repeating the steps until the first current of the inverter circuit is smaller than or equal to the first maximum working current of the inverter circuit for each inverter circuit in the N inverter circuits. By using the method, the current distribution of the inverter circuit is realized, and the heat loss balance of the inverter circuit can be realized.

In a possible embodiment, the controller is specifically configured, in determining the current sharing factor, to: and determining the ratio of the first difference value and the second difference value as the current distribution coefficient of the inverter circuit, wherein the first difference value is the difference value between the preset maximum junction temperature and the junction temperature of the switching device of the inverter circuit, the second difference value is the difference value between a first parameter and a second parameter, the first parameter is the product of N and the preset maximum junction temperature, and the second parameter is the sum of the junction temperatures of the switching devices of the N inverter circuits.

In the embodiment of the present invention, when determining the current distribution coefficients of the N inverter circuits, a ratio between a first difference and a second difference corresponding to the inverter circuits is used as the current distribution coefficient of the inverter circuit, where in the N inverter circuits, the larger the junction temperature of the switching device of the inverter circuit is, the smaller the current distribution coefficient corresponding to the inverter circuit is, and conversely, the smaller the junction temperature of the switching device of the inverter circuit is, the larger the current distribution coefficient corresponding to the inverter circuit is, so that current distribution targeting junction temperature equalization of the inverter circuit can be achieved.

In a possible embodiment, when the total scheduled current comprises a total scheduled reactive current and a total scheduled active current, the first current comprises a first reactive current and a first active current, and the controller is specifically configured to, in determining the first current of each of the at least two inverter circuits: determining a first reactive current of each of the at least two inverter circuits according to the junction temperature of the switching device, the preset maximum junction temperature and the total scheduling reactive current of each of the at least two inverter circuits, wherein for each of the at least two inverter circuits, the first reactive current of the inverter circuit is less than or equal to a first maximum working current of the inverter circuit; and determining a first active current of each of the at least two inverter circuits according to the junction temperature of the switching device of each of the at least two inverter circuits, the preset maximum junction temperature and the total scheduled active current, wherein for each of the at least two inverter circuits, the first active current of the inverter circuit is less than or equal to a second maximum working current of the inverter circuit, and the second maximum working current is a square root of a square difference between the first maximum working current of the inverter circuit and a first reactive current distributed by the inverter circuit.

In the embodiment of the invention, when the current scheduling instruction comprises a reactive current scheduling instruction and an active current scheduling instruction, assuming that the reactive current scheduling instruction is responded preferentially and then the active current scheduling instruction is responded, current distribution is carried out by taking each inverter circuit of at least two inverter circuits as a target when the reactive current scheduling instruction is responded, wherein the first reactive current of the inverter circuit is less than or equal to the first maximum working current of the inverter circuit; when an active current dispatching instruction is responded, current distribution is carried out by taking each inverter circuit in at least two inverter circuits as a target, wherein the first active current of the inverter circuit is less than or equal to the second maximum working current of the inverter circuit, and the second maximum working current is determined according to the first maximum working current of the inverter circuit and the distributed first inactive current of the inverter circuit; therefore, current distribution of the inverter circuits can be realized, and heat loss balance of each inverter circuit can be guaranteed.

In a possible embodiment, the controller is specifically configured to, in terms of determining the first reactive current of each of the at least two inverter circuits according to the junction temperature of the switching device of each of the at least two inverter circuits, the preset maximum junction temperature, and the total scheduled reactive current, determine: determining a current distribution coefficient of each inverter circuit in the N inverter circuits according to the junction temperature of a switching device of each inverter circuit in the N inverter circuits and the preset maximum junction temperature, wherein N is more than or equal to 2; according to the current distribution coefficient and the total dispatching reactive current I of each inverter circuit₂Determining a first reactive current of each inverter circuit; determining that when N first inverter circuits with first reactive current of the inverter circuit larger than first maximum working current of the inverter circuit exist in the N inverter circuits, wherein N is an integer, setting the first reactive current of each first inverter circuit in the N first inverter circuits as the first maximum working current of the first inverter circuit; let N be N-N, I₂＝I₂A, a is the sum of the first maximum working currents of the N first inverter circuits, and the above steps are repeatedly performed until each inverter circuit in the N inverter circuits has a first reactive current less than or equal to the first maximum working current of the inverter circuit.

In the embodiment of the present invention, the method for determining the first reactive current of each inverter circuit when the reactive current scheduling instruction is preferentially responded is the same as the method for determining the first current of each inverter circuit when the current scheduling instruction is only the reactive current scheduling instruction or the active current scheduling instruction, and details thereof are not repeated.

In a possible embodiment, the controller is specifically configured to, in terms of determining the first active current of each of the at least two inverter circuits according to the junction temperature of the switching device, the preset maximum junction temperature, and the total scheduled active current of each of the at least two inverter circuits: determining a current distribution coefficient of each inverter circuit in the N inverter circuits according to the junction temperature of a switching device of each inverter circuit in the N inverter circuits and the preset maximum junction temperature, wherein N is more than or equal to 2; according to the current distribution coefficients and the total scheduling active current I of the N inverter circuits₃Determining a first active current of each of the N inverter circuits; when m second inverter circuits with first active current of the inverter circuits larger than second maximum working current of the inverter circuits exist in the N inverter circuits, m is an integer, the first active current of each second inverter circuit in the m second inverter circuits is set as the second maximum working current of the second inverter circuit, wherein the second maximum working current of the inverter circuits is determined according to the first maximum working current of the inverter circuits and the first inactive current of the inverter circuits; let N be N-m, I₃＝I₃B, b is the sum of the second maximum working currents of the m second inverter circuits, and the above steps are repeatedly performed until each inverter circuit in the N inverter circuits has a first active current less than or equal to the second maximum working current of the inverter circuit.

In the embodiment of the present invention, after the priority response to the reactive current scheduling command is completed, the method of determining the first active current of each inverter circuit in response to the active current scheduling command is similar to the method of determining the first inactive current of each inverter circuit, except that when the first active current of the inverter circuit is greater than the second maximum operating current of the inverter circuit, the first active current of the inverter circuit is set to the second maximum operating current, where the second maximum operating current of the inverter circuit is the square root of the square difference between the first maximum operating current of the inverter circuit and the first inactive current of the inverter circuit.

In a possible embodiment, when the total scheduled current comprises a total scheduled reactive current and a total scheduled active current, the first current comprises a first reactive current and a first active current, and the controller is specifically configured to, in determining the first current of each of the at least two inverter circuits: determining a first active current of each of the at least two inverter circuits according to the junction temperature of a switching device, the preset maximum junction temperature and the total scheduling active current of each of the at least two inverter circuits, wherein for each of the at least two inverter circuits, the first active current of the inverter circuit is less than or equal to the first maximum working current of the inverter circuit; and determining a first reactive current of each of the at least two inverter circuits according to the junction temperature of the switching device of each of the at least two inverter circuits, the preset maximum junction temperature and the total scheduled reactive current, wherein for each of the at least two inverter circuits, the first reactive current of the inverter circuit is less than or equal to a second maximum working current of the inverter circuit, and the second maximum working current is a square root of a square difference between the first maximum working current of the inverter circuit and the first active current distributed by the inverter circuit.

In the embodiment of the present invention, when the current scheduling instruction includes a reactive current scheduling instruction and an active current scheduling instruction, the method may also be a method of preferentially responding to the active current scheduling instruction, then responding to the reactive current scheduling instruction, and preferentially responding to the active allocation and then responding to the reactive allocation, which is similar to the method of preferentially responding to the reactive allocation and then responding to the active allocation, and is not repeated here.

In a possible embodiment, when the total scheduled current comprises a total scheduled reactive current and a total scheduled active current, the first current comprises a first reactive current and a first active current, and the controller is specifically configured to, in determining the first current of each of the at least two inverter circuits: determining a first reactive current of each of the at least two inverter circuits according to the junction temperature of the switching device, the preset maximum junction temperature and the total scheduling reactive current of each of the at least two inverter circuits, and determining a first reactive current of each of the at least two inverter circuits according to the junction temperature of the switching device, the preset maximum junction temperature and the total scheduling reactive current of each of the at least two inverter circuits; wherein, for each of the at least two inverter circuits, the square root of the sum of the squares of the first reactive current and the first active current of the inverter circuit is less than or equal to the first maximum operating current of the inverter circuit.

In the embodiment of the present invention, when the current scheduling instruction includes a reactive current scheduling instruction and an active current scheduling instruction, the method may also be a method for determining the first active current and the first idle current of the inverter circuit in response to the active current scheduling instruction and the reactive current scheduling instruction at the same time, which is similar to the method for determining the first current of each inverter circuit when the current scheduling instruction is the reactive current scheduling instruction or the active current scheduling instruction, except that, in response to the active allocation and the idle allocation at the same time, the current allocation is performed with a goal that the square root of the sum of the squares of the first idle current and the first active current of at least two inverter circuits is less than or equal to the first maximum operating current of the inverter circuit.

In one possible embodiment, the controller is any one of at least two inverter circuits. In the embodiment of the present invention, the controller may be implemented by using any one of at least two inverter circuits in the system.

In one possible embodiment, the system further comprises at least two dc power sources, each of the at least two dc power sources supplying power to the at least one inverter circuit.

In one possible embodiment, the system further includes at least two filters in one-to-one correspondence with the at least two inverter circuits, and the filters are used for filtering the output currents of the inverter circuits.

In the embodiment of the invention, the alternating current filter is arranged, so that harmonic waves generated by the power electronic switching device control system can be filtered out, and adverse effects on an alternating current transmission system are avoided. The alternating current filter can be composed of a capacitor, a reactor, a resistor and the like which are connected in series and in parallel.

Correspondingly, the embodiment of the application also provides a control method, which is applied to the grid-connected system with the multiple parallel inverter circuits, and the method comprises the following steps: and controlling the output current of each of the at least two inverter circuits according to the junction temperature of the at least one switching device of each of the at least two inverter circuits, so that the difference between the junction temperature of the at least one switching device of any one of the at least two inverter circuits and the junction temperature of the at least one switching device of any one of the at least two inverter circuits is less than or equal to a difference threshold value.

According to the control method provided by the embodiment of the invention, the current is flexibly distributed based on the junction temperature of the switching device, the heat loss balance control of each inverter circuit in the grid-connected system can be realized, the service life of the inverter circuit is ensured, and the active maximum capacity output of the grid-connected system can be realized.

In one possible embodiment, the control method further includes: and determining the junction temperature of a switching device of the inverter circuit at the t +1 moment according to the operation parameters and the parameters of the switching device of the inverter circuit at the t moment, wherein the parameters of the switching device are the characteristic parameters of the switching device in the inverter circuit. The operation parameters comprise at least one of active current, reactive current, apparent current, direct current bus voltage, thermal resistance coefficient of the inverter circuit, switching frequency of a switching device of the inverter circuit, modulation wave and detection temperature.

In a possible embodiment, controlling the output current of each of the at least two inverter circuits specifically includes the following steps: controlling each of the at least two inverter circuits to output a first current according to the junction temperature of the switching device of each of the at least two inverter circuits, the preset maximum junction temperature and the total scheduled current of the system, wherein for each of the at least two inverter circuits, the first current of the inverter circuit is less than or equal to the maximum working current of the inverter circuit; the junction temperature of the switching device of the inverter circuit is the junction temperature of any one of the at least one switching device of the inverter circuit or the junction temperature of the switching device of which the junction temperature meets the preset condition.

Drawings

The drawings used in the embodiments of the present application are described below.

Fig. 1 is a schematic flow chart of a control method according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a grid-connected system of multiple parallel inverter circuits according to an embodiment of the present invention;

fig. 3a and fig. 3b are schematic diagrams of a current distribution flow of a multi-parallel inverter circuit grid-connected system according to an embodiment of the present invention;

fig. 4a and 4b are waveforms of junction temperatures of a switching device according to an embodiment of the present invention;

fig. 5a and 5b are waveform diagrams of active power provided by an embodiment of the present invention;

fig. 6a and 6b are waveform diagrams of reactive power provided by an embodiment of the present invention.

Detailed Description

The technical solution in the present application will be described below with reference to the accompanying drawings.

In the present application, "at least one" means one or more, "a plurality" means two or more. "and/or" describes the association relationship of the associated objects, meaning that there may be three relationships, e.g., a and/or B, which may mean: a exists alone, A and B exist simultaneously, and B exists alone, wherein A and B can be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of the singular or plural items. For example, at least one (one) of a, b, or c, may represent: a, b, c, a-b, a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple. In addition, the embodiments of the present application use the words "first", "second", etc. to distinguish between similar items or items having substantially the same function or effect. For example, the first inverter circuit and the second inverter circuit are only for distinguishing different inverter circuits, and the order of the inverter circuits is not limited. Those skilled in the art will appreciate that the words "first," "second," and the like do not limit the number or order of execution.

It is noted that the words "exemplary," "for example," and "such as" are used herein to mean serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" or "e.g.," is not necessarily to be construed as preferred or advantageous over other embodiments or designs. Rather, use of the word "exemplary" or "such as" is intended to present concepts related in a concrete fashion.

In the present application, the inverter circuit is an ac/dc converter, which is a power converter that converts dc power into ac power through power electronics technology. Generally, an inverter circuit performs an inverting function by controlling on and off of a power electronic switching device (simply referred to as a switching device in this application) in the inverter circuit. The multiple parallel inverter circuit in the present application refers to an inverter circuit having parallel ac sides.

Junction Temperature (Junction Temperature) is the actual operating Temperature of the semiconductors in the electronic device. Junction temperature of the power electronic switching device (switching device junction temperature for short) is a key index for safe and reliable operation of the power electronic switching device, so that the junction temperature of the switching device does not exceed the maximum allowable junction temperature in the operation process of the inverter circuit.

Since there is a phase difference between current and voltage in alternating current, the current can be decomposed into two parts according to vector analysis: the voltage is in phase with the "active current", and the voltage is 90 degrees before or after the "reactive current". In short, the current can be decomposed into a real component and a reactive component.

In the prior art, in a grid-connected system of a plurality of parallel inverter circuits, the technical problem of maximally transmitting active power and protecting the service life of the inverter circuits is worth researching. Therefore, the multi-parallel inverter circuit grid-connected system can achieve balanced control of heat loss of each inverter circuit in the grid-connected system, guarantee the service life of the inverter circuits, and achieve maximum active power output of the grid-connected system.

The grid-connected system of the multiple parallel inverter circuits is specifically described below, the grid-connected system comprises a controller and at least two inverter circuits, the at least two inverter circuits comprise input ends and output ends, the output ends of the at least two inverter circuits are connected in parallel, the input ends of the at least two inverter circuits are respectively connected with a direct current input, and the inverter circuits comprise at least one switching device; and a controller for executing the control method 100, referring to fig. 1, fig. 1 is a schematic flow chart of a control method according to an embodiment of the present invention; the control method 100 includes:

101: and acquiring junction temperature of at least one switching device of each of the at least two inverter circuits.

Specifically, the controller may obtain the junction temperature of at least one switching device of each of the at least two inverter circuits in the grid-connected system in a plurality of manners, which may refer to the detailed description in the following paragraphs and are not repeated herein. When the inverter circuit comprises more than two switching devices, the junction temperature of at least one switching device in the more than two switching devices is obtained.

102: and controlling the output current of each of the at least two inverter circuits according to the junction temperature of the at least one switching device of each of the at least two inverter circuits, so that the difference between the junction temperature of the at least one switching device of any one of the at least two inverter circuits and the junction temperature of the at least one switching device of any one of the at least two inverter circuits is less than or equal to a difference threshold value.

Specifically, when it is required to control at least two inverters in the grid-connected system to output a current (i.e., a total scheduled current) of a certain magnitude in parallel, the controller may control the output current of each of the at least two inverter circuits according to the junction temperature of at least one switching device of each of the at least two inverter circuits, so as to implement current scheduling, and enable the junction temperatures of the at least two inverter circuits to be balanced, where junction temperature balancing refers to junction temperature balancing of the switching devices, where "balancing" should be understood that a difference between the junction temperature of at least one switching device of any one of the at least two inverter circuits and the junction temperature of at least one switching device of any one of the at least two inverter circuits is less than or equal to a difference threshold, and a specific value of the difference threshold may be set according to an actual situation, without any particular limitation. More specifically, when the controller controls the at least two inverter circuits to output the total scheduling current in parallel according to the junction temperature of the switching device of the inverter circuits, the controller determines the current (i.e., the first current appearing below) that each of the at least two inverter circuits needs to respond, i.e., the current needs to be output, according to the junction temperature of the switching device, and issues a current distribution instruction to each inverter circuit according to the current, so that the at least two inverter circuits output the total scheduling current, and the sum of the first currents of the at least two inverter circuits is the total scheduling current. The controller receives the current scheduling instruction and then responds the current scheduling instruction to control at least two inverter circuits in the system to output the total scheduling current in parallel.

In the grid-connected system of the multiple parallel inverter circuits in the embodiment of the invention, the controller flexibly distributes current based on the junction temperature of the switching device, so that the heat loss balance (namely junction temperature balance) control of each inverter circuit in the grid-connected system can be realized, the service life of the inverter circuit can be ensured, and the active maximum capacity output of the grid-connected system can be realized.

In one possible embodiment, the grid-connected system further includes at least two dc power sources, each of the at least two dc power sources supplying power to the at least one inverter circuit. In another possible embodiment, the system further includes at least two filters in one-to-one correspondence with the at least two inverter circuits, and the filters are used for filtering the output currents of the inverter circuits, that is, the filters are ac filters. In the embodiment of the invention, the alternating current filter is arranged, so that harmonic waves generated by the power electronic switching device control system can be filtered out, and adverse effects on an alternating current transmission system are avoided. The alternating current filter can be composed of a capacitor, a reactor, a resistor and the like which are connected in series and in parallel. In addition, the system can also comprise transformers, and the output ends of at least two inverter circuits are connected with the input ends of the transformers, wherein the number of the transformers is more than one.

Referring to fig. 2, fig. 2 is a schematic structural diagram of a multiple parallel inverter circuit grid-connected system according to an embodiment of the present invention; fig. 2 illustrates a possible grid-connected system of multiple parallel inverter circuits, wherein the grid-connected system 200 includes four inverter circuits (inverter circuit 1, inverter circuit 2, inverter circuit 3, and inverter circuit 4, respectively), four dc power supplies (dc power supply 201 and dc power supply 203), four filters (filter 1, filter 2, filter 3, and filter 4, respectively), and a transformer 202. Each dc power supply correspondingly supplies power to an inverter circuit, and taking the dc power supply 201 and the dc power supply 203 as an example, the dc power supply 201 supplies power to the inverter circuit 1, and the dc power supply 203 supplies power to the inverter circuit 2. Each inverter circuit is provided with a filter, for example, the inverter circuit 1 corresponds to the filter 1, and the inverter circuit 2 corresponds to the filter 2. In addition, the transformation ratio of the transformer 202 is k, and the transformer 202 has two primary windings, wherein the output currents of the inverter circuit 1 and the inverter circuit 3 are filtered and then input in parallel to one primary winding of the transformer 202, and the output currents of the inverter circuit 2 and the inverter circuit 4 are filtered and then input in parallel to the other primary winding of the transformer 202. After voltage conversion by the transformer 202, is incorporated into the grid. In particular, it is assumed that after being scheduled by the controller, the inverter circuit 1, the inverter circuit 2, the inverter circuit 3, and the inverter circuit 4 respectively need to output currents i₁、i₂、i₃And i₄Then the output current after the transformation process of the transformer 202 is i_sumThe current satisfies the following relationship: i.e. i_sum＝(i₁+i₂+i₃+i₄) K is the sum of the values of k and k. In addition, in this embodiment, a dc filter is further disposed between the inverter circuit and the dc power supply to stabilize the dc input voltage and implement energy buffering.

In the embodiment of the invention, when the junction temperature of the switching device of the inverter circuit is obtained, the junction temperature of the switching device of each inverter circuit in the grid-connected system can be determined, and then the junction temperature of the switching device is transmitted to the controller by the inverter circuit for processing, so that the heat loss balance control of each inverter circuit in the grid-connected system is realized based on a master-slave control framework. The junction temperature of the switching device of each inverter circuit in the grid-connected system can be determined by the controller, and the heat loss balance control of the inverter circuits is realized according to the junction temperature of the switching devices, so that the links of data transmission can be reduced, and the accuracy of junction temperature data is ensured.

In one possible embodiment, the controller or the inverter circuit is specifically configured to, in determining the junction temperature of the switching device of the inverter circuit: and determining junction temperature of a switching device of the inverter circuit at the t +1 moment according to the operation parameters and the parameters of the switching device of the inverter circuit at the t moment, wherein the parameters of the switching device are characteristic parameters (such as switching characteristic parameters and the like) of the switching device in the inverter circuit. The operation parameters comprise at least one of active current of the inverter circuit, reactive current of the inverter circuit, apparent current of the inverter circuit, direct-current bus voltage of the inverter circuit, thermal resistance coefficient of the inverter circuit, switching frequency of a switching device of the inverter circuit, modulation wave of the switching device and detection temperature of the switching device.

Specifically, the apparent current of the inverter circuit is equal to the square root of the sum of the squares of the active current and the reactive current of the inverter circuit. The modulation wave of the switching device refers to a modulation waveform of the switching device, and when the junction temperature of the switching device is determined, the junction temperature of the switching device of the inverter circuit at the time t +1 can be determined according to other operation parameters such as a modulation signal corresponding to the time t and the parameters of the switching device of the inverter circuit. And the detected temperature of the switching device can be obtained using a thermistor. In the embodiment of the invention, the junction temperature of the switching device of the inverter circuit at the t +1 moment is predicted according to the operation parameters of the inverter circuit at the t moment and the parameters of the switching device, so that the balance of heat loss of the inverter circuit is further controlled according to the junction temperature of the switching device, the junction temperature of the switching device is controlled in a safe range, and the inverter circuit can operate safely and reliably. Further specifically, the inverter circuit may acquire an operation parameter of the inverter circuit itself at the time t, and determine the junction temperature of the switching device of the inverter circuit at the time t +1 according to the operation parameter and the switching device parameter thereof. In addition, the operation parameters of the inverter circuit can be acquired in real time through the acquisition device, and the acquisition device sends the operation parameters to the inverter circuit or the controller so as to predict the junction temperature according to the operation parameters and the parameters of the switching device; when the junction temperature prediction is performed by the controller, the acquisition device may be an inverter circuit. It is noted that for each switching device in the inverter circuit, the junction temperature of each switching device may be determined using the methods described above.

It is particularly noted that, in the embodiment of the present invention, the operation parameters may include an active current of the inverter circuit, a reactive current of the inverter circuit, a dc bus voltage of the inverter circuit, a thermal resistivity of the inverter circuit, a switching frequency of a switching device of the inverter circuit, a modulation wave of the switching device, and a detected temperature of the switching device, and of course, the operation parameters may also include an apparent current of the inverter circuit, a dc bus voltage of the inverter circuit, a thermal resistivity of the inverter circuit, a switching frequency of a switching device of the inverter circuit, a modulation wave of the switching device, and a detected temperature of the switching device; alternatively, the operating parameters of the inverter circuit may be other possible components, and are not particularly limited in this application.

Further, referring to fig. 3a and 3b, fig. 3a and 3b are schematic diagrams of a current distribution flow of a grid-connected system of multiple parallel inverter circuits according to an embodiment of the present invention; in fig. 3a, the grid-connected system includes N inverter circuits, the inverter circuit 1 is taken as an example for specific description, the controller is taken as an example for determining the junction temperature of the switching devices of the inverter circuits, it is assumed that the parameters of the switching devices of all the switching devices in the inverter circuit 1 are the same, the inverter circuit 1 collects the operating parameters of itself and transmits the operating parameters to the controller 201, and in addition, the controller 201 can obtain the switching device of each inverter circuit in the grid-connected systemThe characteristic parameters of the piece. In this way, the controller 201 can predict the junction temperature of the switching device of the inverter circuit 1 at the time t +1 according to the operating parameter of the inverter circuit 1 at the time t and the switching device parameter of the inverter circuit 1. For other inverter circuits, the junction temperature of the switching device at the time t +1 can be obtained as well. After the controller 201 receives the current scheduling instruction, according to junction temperatures of the switching devices of all the inverter circuits at the time t +1, and with the junction temperature equalization of the power electronic switching devices of each inverter circuit as a target, determining the current required to be output by each inverter circuit, and issuing a current distribution instruction to the corresponding inverter circuit according to the current. Referring to fig. 3b, taking time k as an example, at time k, each inverter circuit controls the active and/or reactive current output according to the current distribution command issued by the controller in the last beat (time k-1), that is, executes the current distribution command i_ref(k-1) (i.e., the current sharing command calculated at time k-1); in addition, the controller predicts the junction temperature of the switching device at the moment k +1 of the switching device according to the current operating parameters (at the moment k) of the inverter circuit, and then determines the current distribution instruction i (at the moment k + 1) of the next beat of each inverter circuit according to the predicted junction temperature of the switching device_ref(k) And further closed-loop control is realized.

Furthermore, taking the controller to determine the junction temperature of the switching device at the k +1 moment of the inverter circuit as an example, wherein taking one switching device in the inverter circuit as an example, and taking the operating parameters including active current, reactive current, direct current bus voltage, thermal resistance coefficient, switching frequency, modulation wave and detected temperature as an example; the controller calculates the total loss P of the switching device at the moment k first_lossTotal loss P of switching device_lossIncluding the turn-on loss E_onTurn-off loss E_offAnd conduction loss E_conWherein the total loss P_lossThe general calculation formula of (a) is as follows:

P_loss＝g(i_d，i_q，U_bus，M，f_s，c)

where g () is the switching device loss calculation function, i_dIs an active current, i_qIs a reactive current, U_busIs the DC bus voltage, f_sTo openThe off frequency, M is the modulation wave, and c is the switching device parameter.

Next, the junction temperature of the switching device at time k +1 can be predicted as:

T_j＝T_NTC+R_j*P_loss

wherein, T_jIs the junction temperature, T, of the switching device_NTCFor sensing temperature, R, of switching devices_jIs the thermal resistivity of the inverter circuit.

In particular, the switching device loss calculation function means that the loss of the switching device can be determined according to the active current, the reactive current, the direct current bus voltage, the switching frequency, the modulation wave and the switching device parameter, and in fact, the loss of the switching device can be determined by using a table lookup method or a curve fitting calculation method, for example, and the switching loss E is hereinafter referred to as the turn-on loss E_onFor example, the inverter circuit collects the output current in real time according to the current instantaneous apparent current i, the DC bus voltage and the switching frequency f_sAt the moment of conducting signals to the switching device, the current instantaneous turn-on loss can be inquired according to a turn-on loss curve or a turn-on loss table of the switching device, the instantaneous turn-on loss inquired in real time is subjected to integral accumulation, and the turn-on loss E of one period is calculated_on. Other loss determination methods may refer to the determination method of the opening loss.

In some possible embodiments, the controller is any one of at least two inverter circuits. In the embodiment of the invention, the controller can be realized by adopting any one of at least two inverter circuits in the system, and the controller is not required to be additionally arranged, so that the cost required by current distribution of a grid-connected system can be reduced. In practice, each inverter circuit has a main control circuit (e.g., a processor or a controller) to control the inversion process of the inverter circuit, or more than two inverter circuits share a main control circuit. Therefore, at least one main control circuit of the at least two inverter circuits may function as the controller.

In one possible embodiment, the controller is specifically configured to, in controlling the output current of each of the at least two inverter circuits: controlling each of the at least two inverter circuits to output a first current according to the junction temperature of the switching device of each of the at least two inverter circuits, the preset maximum junction temperature and the total scheduling current, wherein for each of the at least two inverter circuits, the first current of the inverter circuit is less than or equal to the maximum working current of the inverter circuit; the junction temperature of the switching device of the inverter circuit is the junction temperature of any one of the at least one switching device of the inverter circuit or the junction temperature of the switching device of which the junction temperature meets the preset condition.

In the embodiment of the present invention, as for the junction temperature of the switching device, the junction temperature of any one switching device in at least one switching device in the inverter circuit may be used as the junction temperature of the switching device of the inverter circuit. The preset condition may be that the junction temperature is the maximum, that is, the maximum junction temperature of all the switching devices in the inverter circuit is used as the junction temperature of the switching device of the inverter circuit. The preset conditions may be adjusted according to actual conditions, and are not particularly limited. In addition, after the controller receives the current scheduling instruction, the controller controls each of the at least two inverter circuits to output a first current according to the junction temperature of the switching device, the preset maximum junction temperature and the total scheduling current of the at least two inverter circuits, namely, the first current which should be output by each inverter circuit in the grid-connected system is distributed to each inverter circuit in the grid-connected system, so that the first current output by each inverter circuit does not exceed the maximum working current of the inverter circuit, the active power generation loss caused by maximum capacity limitation and heat derating is reduced, the active power generation output of the grid-connected system can be realized, the heat loss balance of each inverter circuit can be realized, and the service life reduction loss of the inverter circuit caused by heavy load or overheating is reduced.

In one possible embodiment, when the current scheduling instruction is a reactive current scheduling instruction or an active current scheduling instruction, correspondingly, the reactive current scheduling instruction carries total scheduling reactive current information, and the total scheduling current at this time is total scheduling reactive current; the active current scheduling instruction carries total scheduling active current information, and the total scheduling current at the moment is the total scheduling active current. When the total scheduled current is the total scheduled reactive current or the total scheduled active current, the controller is specifically configured to, in determining the first current of each of the at least two inverter circuits:

a1: determining a current distribution coefficient of each inverter circuit in the N inverter circuits according to the junction temperature of a switching device of each inverter circuit in the N inverter circuits and the preset maximum junction temperature, wherein N is more than or equal to 2; according to the current distribution coefficient and the total scheduling current I of each inverter circuit₁A first current is determined for each inverter circuit.

Specifically, the preset maximum junction temperature refers to a maximum allowable junction temperature of the switching device, and a specific value of the preset maximum junction temperature may be set according to an actual situation, without any particular limitation. And the controller is used for determining the current distribution coefficient specifically: and determining the ratio of the first difference value and the second difference value as the current distribution coefficient of the inverter circuit, wherein the first difference value is the difference value between the preset maximum junction temperature and the junction temperature of the switching device of the inverter circuit, the second difference value is the difference value between a first parameter and a second parameter, the first parameter is the product of N and the preset maximum junction temperature, and the second parameter is the sum of the junction temperatures of the switching devices of the N inverter circuits. In the N inverter circuits, the larger the junction temperature of a switching device of the inverter circuit is, the smaller the current distribution coefficient corresponding to the inverter circuit is; on the contrary, the smaller the junction temperature of the switching device of the inverter circuit is, the larger the current distribution coefficient corresponding to the inverter circuit is, so that the current distribution targeting the junction temperature balance of the inverter circuit can be realized. Further, according to the current distribution coefficient and the total scheduling current I of each inverter circuit₁A first current is determined for each inverter circuit.

In the following, taking an example that the grid-connected system has N inverter circuits, the current distribution coefficient of each inverter circuit is as follows:

wherein, T_jMaxFor presetting the maximum junction temperature, T_j1Junction temperature, T, of switching device of the 1 st inverter circuit_j2Junction temperature, T, of switching device of the No. 2 inverter circuit_jNJunction temperature of switching device of Nth inverter circuit, N is the number of inverter circuits in parallel network system of multiple parallel inverter circuits, Coef₁For the current distribution coefficient, Coef, of the 1 st inverter circuit_NAnd distributing the coefficient for the current of the Nth inverter circuit. Wherein, N current distribution coefficients satisfy the following conditions:

Coef₁+Coef₂+…+Coef_N＝1

the first current of the inverter circuit is:

i_refN＝Coef_N*i_ref

wherein i_refNFirst current of Nth inverter circuit, i_refAnd the total current of the grid-connected system of the multiple parallel inverter circuits is scheduled.

A2: determining that when N first inverter circuits with first currents of the inverter circuits larger than the maximum working current of the inverter circuit exist in the N inverter circuits, and N is an integer, setting the first current of each first inverter circuit in the N first inverter circuits as the first maximum working current of the first inverter circuit; let N be N-N, I₁＝I₁A, a is the sum of the first maximum working currents of the N first inverter circuits, and the above steps are repeatedly performed until each inverter circuit in the N inverter circuits has a first current less than or equal to the first maximum working current of the inverter circuit.

Specifically, each inverter circuit has an operating current range, and correspondingly has a minimum operating current and a maximum operating current, which is the first maximum operating current in the present application. The first maximum operating currents of the inverter circuits may be the same or different. After the first current of each inverter circuit is determined through the step A1, the first maximum working current i of each inverter circuit is determined_MaxAnd a first current i corresponding to the inverter circuit_refNComparing to determine the first current i of the inverter circuit_refNIs larger than the first maximum working current i of the inverter circuit_MaxAnd limiting the first current of the inverter circuit exceeding the maximum capacity (i.e., the n first inverter circuits) to its corresponding i_MaxAnd redistributing the remaining total dispatching current (i.e. the current remaining after subtracting the sum of the first maximum operating currents of the N first inverter circuits from the total dispatching current) to the remaining inverter circuits (the inverter circuits except the N first inverter circuits in the N inverter circuits) according to the method of the step a1 until all inverter circuit current commands are distributed, and enabling the first currents of the inverter circuits in the grid-connected system to satisfy: i.e. i_refN≤i_Max。

By using the method, the active current or reactive current distribution of the inverter circuit is realized, and the heat loss balance of the inverter circuit can be realized.

In another possible embodiment, when the total scheduled current comprises a total scheduled reactive current and a total scheduled active current, the first current comprises a first reactive current and a first active current, i.e. the first reactive current is a reactive component of the first current and the first active current is an active component of the first current. The controller is specifically configured to, in determining the first current of each of the at least two inverter circuits:

b1: determining a first reactive current of each of the at least two inverter circuits according to the junction temperature of the switching device of each of the at least two inverter circuits, the preset maximum junction temperature and the total scheduling reactive current, wherein for each of the at least two inverter circuits, the first reactive current of the inverter circuit is less than or equal to a first maximum working current of the inverter circuit: and

b2: and determining a first active current of each of the at least two inverter circuits according to the junction temperature of the switching device, the preset maximum junction temperature and the total scheduled active current of each of the at least two inverter circuits, wherein for each of the at least two inverter circuits, the first active current of the inverter circuit is less than or equal to a second maximum working current of the inverter circuit, and the second maximum working current is a square root of a square difference between the first maximum working current of the inverter circuit and a first reactive current distributed by the inverter circuit.

In the embodiment of the invention, when the current scheduling instruction comprises a reactive current scheduling instruction and an active current scheduling instruction, assuming that the reactive current scheduling instruction is responded preferentially and then the active current scheduling instruction is responded, current distribution is carried out by taking each inverter circuit of at least two inverter circuits as a target when the reactive current scheduling instruction is responded, wherein the first reactive current of the inverter circuit is less than or equal to the first maximum working current of the inverter circuit; when an active current dispatching instruction is responded, current distribution is carried out by taking each inverter circuit in at least two inverter circuits as a target, wherein the first active current of the inverter circuit is less than or equal to the second maximum working current of the inverter circuit, and the second maximum working current is determined according to the first maximum working current of the inverter circuit and the distributed first inactive current of the inverter circuit; at this time, the second maximum working current of the inverter circuit is the first maximum working current i of the inverter circuit_MaxAnd the first reactive current i distributed by the inverter circuit_1qThe square root of the square difference of (i.e.

Therefore, the current distribution of the inverter circuit can be realized, and the heat loss balance of the inverter circuit can be realized.

Further, the controller is specifically configured to, in terms of determining the first reactive current of each of the at least two inverter circuits according to the junction temperature of the switching device of each of the at least two inverter circuits, the preset maximum junction temperature, and the total scheduled reactive current:

determining a current distribution coefficient of each inverter circuit in the N inverter circuits according to the junction temperature of a switching device of each inverter circuit in the N inverter circuits and the preset maximum junction temperature, wherein N is more than or equal to 2; according to the current distribution coefficient and the total dispatching reactive current I of each inverter circuit₂Determining a first reactive current of each inverter circuit; determining that, of the N inverter circuits, there is a first reactive current of the inverter circuit greater than a first maximum operating current of the inverter circuitWhen n first inverter circuits are used, if n is an integer, setting the first reactive current of each first inverter circuit in the n first inverter circuits as the first maximum working current of the first inverter circuit; let N be N-N, I₂＝I₂A, a is the sum of the first maximum working currents of the N first inverter circuits, and the above steps are repeatedly performed until each inverter circuit in the N inverter circuits has a first reactive current less than or equal to the first maximum working current of the inverter circuit.

In the embodiment of the present invention, the method for determining the first reactive current of each inverter circuit when the reactive current scheduling instruction is preferentially responded is the same as the method for determining the first current of each inverter circuit when the current scheduling instruction is the reactive current scheduling instruction or the active current scheduling instruction, and details thereof are not repeated.

Further, the controller is specifically configured to, in terms of determining the first active current of each of the at least two inverter circuits according to the junction temperature of the switching device of each of the at least two inverter circuits, the preset maximum junction temperature, and the total scheduled active current:

determining a current distribution coefficient of each inverter circuit in the N inverter circuits according to the junction temperature of a switching device of each inverter circuit in the N inverter circuits and the preset maximum junction temperature, wherein N is more than or equal to 2; according to the current distribution coefficients and the total scheduling active current I of the N inverter circuits₃Determining a first active current of each of the N inverter circuits; determining that when m second inverter circuits with first active current of the inverter circuits larger than second maximum working current of the inverter circuits exist in the N inverter circuits, wherein m is an integer, setting first active current of each second inverter circuit in the m second inverter circuits as second maximum working current of the second inverter circuit, wherein the second maximum working current of the inverter circuits is square root of square difference of the first maximum working current of the inverter circuits and the first inactive current of the inverter circuits; let N be N-m, I₃＝I₃B, b is the sum of the second maximum working currents of the m second inverter circuits, and the above steps are repeatedly performed until each inverter circuit in the N inverter circuits invertsThe first active current of the circuit is less than or equal to the second maximum working current of the inverter circuit.

In the embodiment of the present invention, after the reactive current scheduling command is preferentially responded, the method of determining the first active current of each inverter circuit in response to the active current scheduling command is similar to the method of determining the first inactive current of each inverter circuit, except that when the first active current of the inverter circuit is greater than the second maximum operating current of the inverter circuit, the first active current of the inverter circuit is set to the second maximum operating current.

In a further possible embodiment, when the total scheduled current comprises a total scheduled reactive current and a total scheduled active current, the first current comprises a first reactive current and a first active current, the controller is specifically configured to, in determining the first current of each of the at least two inverter circuits:

c1: determining a first active current of each of the at least two inverter circuits according to the junction temperature of a switching device, the preset maximum junction temperature and the total scheduling active current of each of the at least two inverter circuits, wherein for each of the at least two inverter circuits, the first active current of the inverter circuit is less than or equal to the first maximum working current of the inverter circuit; and

c2: determining a first reactive current of each of at least two inverter circuits according to junction temperature of a switching device, preset maximum junction temperature and total scheduling reactive current of each of the at least two inverter circuits, wherein for each of the at least two inverter circuits, the first reactive current of the inverter circuit is less than or equal to a second maximum working current of the inverter circuit, the second maximum working current is determined according to the first maximum working current of the inverter circuit and the first active current distributed by the inverter circuit, and at the moment, the second maximum working current of the inverter circuit is the first maximum working current i of the inverter circuit_MaxAnd the first active current i distributed by the inverter circuit_1dThe square root of the square difference of (i.e.

d1: determining a first reactive current of each of the at least two inverter circuits according to the junction temperature of the switching device, the preset maximum junction temperature and the total scheduled reactive current of each of the at least two inverter circuits, an

D2: determining a first active current of each of the at least two inverter circuits according to the junction temperature of a switching device, the preset maximum junction temperature and the total scheduling active current of each of the at least two inverter circuits; wherein, for each of the at least two inverter circuits, the square root of the sum of the squares of the first reactive current and the first active current of the inverter circuit is less than or equal to the first maximum operating current of the inverter circuit.

In the embodiment of the present invention, when the current scheduling instruction includes a reactive current scheduling instruction and an active current scheduling instruction, the method may also be a method for determining a first active current and a first reactive current of the inverter circuit in response to the active current scheduling instruction and the reactive current scheduling instruction at the same time, which is similar to the method for determining a first current of each inverter circuit when the current scheduling instruction is a reactive current scheduling instruction or an active current scheduling instruction, except that when the current scheduling instruction is in response to the active allocation and the reactive allocation at the same time, the method is similar to the method for determining a first current of each inverter circuit in at least two inverter circuits, and the first reactive current i of each inverter circuit is different from the method for determining_1qAnd a first active current i_1dSquare of the sum of squares ofThe first maximum working current i is less than or equal to the inverter circuit_MaxCurrent distribution for the purpose, i.e. each inverter circuit satisfies

Specifically, after the current distribution coefficient is calculated according to the method, the first dead current and the first active current of each of the N inverter circuits can be determined; then, among N inverter circuits, the inverter circuit satisfying

The x third inverter circuits perform the same-proportion down-regulation on the corresponding first reactive current and the corresponding first reactive current for each third inverter circuit (the down-regulation proportion can be set according to actual conditions and is not particularly limited) until the third inverter circuits meet the requirement

The magnitude of the first reactive current and the first active current down-regulated by each third inverter circuit can be determined. Then, taking the total scheduled active current as an example, the difference value between the total scheduled active current and the sum of the first active current adjusted down by the x third inverter circuits is redistributed to the inverter circuits except the x third inverter circuits in the N inverter circuits, and the steps are repeatedly executed until each inverter circuit in the N inverter circuits meets the requirement

Further, when the first reactive current and the first reactive current of the third inverter circuit are down-regulated in the same proportion, the first reactive current and the first reactive current of the third inverter circuit may be multiplied by a maximum limiting coefficient, respectively, to update the first reactive current and the first reactive current of the third inverter circuit, where the updated first reactive current and the updated first reactive current are smaller than the first reactive current and the first reactive current before the down-regulation, and the maximum limiting coefficient is smaller than one. In some possible embodiments, the maximum limiting factor is a ratio of a first maximum operating current of the third inverter circuit to a square root of a sum of squares of a first reactive current and a first active current of the third inverter circuit; in addition, the maximum limiting coefficient may also be a ratio of a third difference value to the first maximum operating current of the third inverter circuit, where the third difference value is a difference value between a square root of a sum of squares of the first dead current and the first active current of the third inverter circuit and the first maximum operating current of the third inverter circuit.

The following specifically describes the control method of the embodiment of the present invention, taking the multi-parallel inverter circuit grid-connected system having two inverter circuits, namely, inverter circuit 1 and inverter circuit 2, as an example:

a. the two inverter circuits carry out self running state detection in real time to obtain various running parameters including active current i_dReactive current i_qDC bus voltage U_busSwitching frequency f_sModulated wave M and detected temperature T_NTCAnd the like, and sends the obtained operating parameters to the controller.

b. When an active current dispatching instruction (carrying total dispatching active current i) is received_drefThe corresponding power is the total scheduled active power P_ref) And a reactive current dispatching instruction (carrying total dispatching reactive current i)_qrefThe corresponding power is the total scheduled reactive power Q_ref) Then, the controller calculates the total loss P of the switching devices of the two inverter circuits in real time according to the operation parameters of the inverter circuits and the parameters of the switching devices_loss1And P_loss2And predicting junction temperature T of switching devices of the two inverter circuits_j1And T_j2。

c. Current distribution control is carried out by taking junction temperature balance of each inverter circuit as a target, and current instruction distribution coefficient Coef of each inverter circuit is calculated₁And Coef₂Furthermore, T can be realized by the control method of the embodiment of the invention_j1And T_j2Referring to fig. 4a and 4b, where fig. 4a and 4b are waveform diagrams of junction temperatures of switching devices according to an embodiment of the present invention, where fig. 4a is a schematic diagram of junction temperature changes of the switching devices of the inverter circuit 1, and fig. 4b is a schematic diagram of junction temperatures of the switching devices of the inverter circuit 1, and fig. 4b is a schematic diagram of inverter power supplyAnd (3) a schematic diagram of the junction temperature of the switching device of the circuit 2. In addition, the inverter circuit 1 and the inverter circuit 2 output different active currents i_d1And i_d2Reactive current i_q1And i_q2Wherein i is_dref＝i_d1+i_d2，i_qref＝i_q1+i_q2(ii) a Correspondingly, the active power output by the inverter circuit 1 and the inverter circuit 2 is P₁And P₂(ii) a The output reactive power is respectively Q₁And Q₂In which P is_ref＝P₁+P₂，Q_ref＝Q₁+Q₂(ii) a Referring to fig. 5a, 5b, 6a, and 6b, fig. 5a and 5b are waveform diagrams of an active power according to an embodiment of the present invention; fig. 6a and 6b are waveform diagrams of reactive power provided by an embodiment of the present invention, fig. 5a is a schematic diagram of a change in active power of the inverter circuit 1, and fig. 5b is a schematic diagram of a change in active power of the inverter circuit 2; fig. 6a is a schematic diagram of the change of the reactive power of the inverter circuit 1, and fig. 6b is a schematic diagram of the change of the reactive power of the inverter circuit 2.

According to the grid-connected system, active power and/or reactive power are/is flexibly distributed based on junction temperature of the switching devices of the inverter circuits, current distribution control is carried out by taking junction temperature balance of the switching devices of the inverter circuits as a target, on one hand, active power maximum capacity output is achieved, and active power generation loss caused by maximum capacity limit and heat derating is reduced; on the other hand, the heat loss balance control (deviation is in a certain range) of the power electronic switching devices of all the inverter circuits is realized, the service life loss of the inverter circuits caused by heavy load or overheating is reduced, and the reliability of the system is improved.

In the embodiments provided in the present application, it should be understood that the disclosed system and method may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment. In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit.

The functions, if implemented in the form of software functional units and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present application or portions thereof that substantially contribute to the prior art may be embodied in the form of a software product stored in a storage medium and including instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: various media capable of storing program codes, such as a usb disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk, or an optical disk.

The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A multi-parallel inverter circuit grid-connected system is characterized by comprising a controller and at least two inverter circuits, wherein the at least two inverter circuits comprise input ends and output ends, the output ends of the at least two inverter circuits are connected in parallel, the input ends of the at least two inverter circuits are respectively connected with a direct current input, the inverter circuits comprise at least one switching device, wherein,

the controller is configured to control an output current of each of the at least two inverter circuits according to a junction temperature of at least one switching device of each of the at least two inverter circuits, so that a difference between the junction temperature of at least one switching device of any one of the at least two inverter circuits and the junction temperature of at least one switching device of any one of the at least two inverter circuits is smaller than or equal to a difference threshold.

2. The system of claim 1, wherein,

the controller is further configured to determine a junction temperature of at least one switching device of each of the at least two inverter circuits;

alternatively, the first and second electrodes may be,

the inverter circuit is used for determining the junction temperature of at least one switching device of the inverter circuit and sending the junction temperature to the controller.

3. The system of claim 2, wherein the controller or the inverter circuit, in determining the inverter circuit junction temperature of the switching device, is specifically configured to:

and determining junction temperature of a switching device of the inverter circuit at the t +1 moment according to the operation parameters and the parameters of the switching device of the inverter circuit at the t moment, wherein the parameters of the switching device are characteristic parameters of the switching device in the inverter circuit.

4. The system of claim 3, wherein the operating parameters comprise at least one of active current, reactive current, apparent current, dc bus voltage, thermal resistivity, switching frequency of switching devices of the inverter circuit, modulated wave, sensed temperature of the inverter circuit.

5. The system according to any one of claims 1 to 4, wherein the controller is configured to, in controlling the output current of each of the at least two inverter circuits, in particular to:

controlling each of the at least two inverter circuits to output a first current according to the junction temperature of the switching device of each of the at least two inverter circuits, the preset maximum junction temperature and the total scheduled current of the system, wherein for each of the at least two inverter circuits, the first current of the inverter circuit is less than or equal to the maximum working current of the inverter circuit; the junction temperature of the switching device of the inverter circuit is the junction temperature of any one of the at least one switching device of the inverter circuit or the junction temperature of the switching device of which the junction temperature meets the preset condition.

6. The system according to claim 5, wherein the controller, in determining the first current of each of the at least two inverter circuits, is specifically configured to, when the total scheduled current is a total scheduled reactive current or a total scheduled active current:

determining a current distribution coefficient of each inverter circuit in the N inverter circuits according to the junction temperature of the switching device of each inverter circuit in the N inverter circuits and the preset maximum junction temperature, wherein N is more than or equal to 2;

according to the current distribution coefficient of each inverter circuit and the total scheduling current I₁Determining the first current of each inverter circuit;

determining that when N first inverter circuits with first currents of the inverter circuits larger than the maximum working current of the inverter circuit exist in the N inverter circuits, wherein N is an integer, setting the first current of each first inverter circuit in the N first inverter circuits as the first maximum working current of the first inverter circuit;

let N be N-N, I₁＝I₁A, the a is the sum of the first maximum operating currents of the N first inverter circuits, and the above steps are repeatedly performed until each inverter circuit in the N inverter circuits has a first current smaller than or equal to the first maximum operating current of the inverter circuit.

7. The system according to claim 6, characterized in that the controller, in determining the current distribution coefficient, is specifically configured to:

determining a ratio between a first difference and a second difference as a current distribution coefficient of the inverter circuit, wherein the first difference is a difference between the preset maximum junction temperature and a junction temperature of a switching device of the inverter circuit, the second difference is a difference between a first parameter and a second parameter, the first parameter is a product of the N and the preset maximum junction temperature, and the second parameter is a sum of the junction temperatures of the switching devices of the N inverter circuits.

8. The system of claim 5, wherein the first current comprises a first reactive current and a first active current when the total scheduled current comprises a total scheduled reactive current and a total scheduled active current, and wherein the controller is specifically configured to, in determining the first current for each of the at least two inverter circuits:

determining the first reactive current of each of at least two inverter circuits according to the junction temperature of the switching device, the preset maximum junction temperature and the total scheduled reactive current of each of the at least two inverter circuits, wherein for each of the at least two inverter circuits, the first reactive current of the inverter circuit is less than or equal to the first maximum working current of the inverter circuit; and

and determining the first active current of each of the at least two inverter circuits according to the junction temperature of the switching device of each of the at least two inverter circuits, the preset maximum junction temperature and the total scheduled active current, wherein for each of the at least two inverter circuits, the first active current of the inverter circuit is less than or equal to a second maximum working current of the inverter circuit, and the second maximum working current is a square root of a square difference between the first maximum working current of the inverter circuit and the first reactive current distributed to the inverter circuit.

9. The system of claim 8, wherein the controller is specifically configured to, in determining the first reactive current for each of the at least two inverter circuits based on a switching device junction temperature, the preset maximum junction temperature, and the total scheduled reactive current for each of the at least two inverter circuits:

according to the current distribution coefficient of each inverter circuit and the total dispatching reactive current I₂Determining the first reactive current of each inverter circuit;

determining that when N first inverter circuits with first reactive current of the inverter circuit larger than first maximum working current of the inverter circuit exist in the N inverter circuits, wherein N is an integer, setting the first reactive current of each first inverter circuit in the N first inverter circuits as the first maximum working current of the first inverter circuit;

let N be N-N, I₂＝I₂A, the a is the sum of the first maximum working currents of the N first inverter circuits, and the above steps are repeatedly performed until each inverter circuit in the N inverter circuits has a first reactive current smaller than or equal to the first maximum working current of the inverter circuit.

10. The system according to claim 8 or 9, wherein the controller is specifically configured to, in determining the first active current for each of the at least two inverter circuits based on a switching device junction temperature, the preset maximum junction temperature, and the total scheduled active current for each of the at least two inverter circuits:

according to the current distribution coefficients of the N inverter circuits and the total scheduling active current I₃Determining the first active current of each of the N inverter circuits;

determining that when m second inverter circuits with first active current of the inverter circuit larger than second maximum working current of the inverter circuit exist in the N inverter circuits, wherein m is an integer, the first active current of each second inverter circuit in the m second inverter circuits is set as the second maximum working current of the second inverter circuit, and the second maximum working current of the inverter circuit is the square root of the square difference of the first maximum working current of the inverter circuit and the first reactive current of the inverter circuit;

let N be N-m, I₃＝I₃And b is the sum of the second maximum working currents of the m second inverter circuits, and the steps are repeatedly executed until each inverter circuit in the N inverter circuits has a first active current smaller than or equal to the second maximum working current of the inverter circuit.

11. The system of claim 5, wherein the first current comprises a first reactive current and a first active current when the total scheduled current comprises a total scheduled reactive current and a total scheduled active current, and wherein the controller is specifically configured to, in determining the first current for each of the at least two inverter circuits:

determining the first active current of each of at least two inverter circuits according to the junction temperature of the switching device, the preset maximum junction temperature and the total scheduled active current of each of at least two inverter circuits, wherein for each of the at least two inverter circuits, the first active current of the inverter circuit is less than or equal to the first maximum working current of the inverter circuit; and

and determining the first reactive current of each of the at least two inverter circuits according to the junction temperature of the switching device of each of the at least two inverter circuits, the preset maximum junction temperature and the total scheduled reactive current, wherein for each of the at least two inverter circuits, the first reactive current of the inverter circuit is less than or equal to a second maximum working current of the inverter circuit, and the second maximum working current is a square root of a square difference between the first maximum working current of the inverter circuit and the first active current distributed by the inverter circuit.

12. The system of claim 5, wherein the first current comprises a first reactive current and a first active current when the total scheduled current comprises a total scheduled reactive current and a total scheduled active current, and wherein the controller is specifically configured to, in determining the first current for each of the at least two inverter circuits:

determining the first reactive current of each of at least two inverter circuits according to the switching device junction temperature, the preset maximum junction temperature and the total scheduled reactive current of each of at least two inverter circuits, and determining the first active current of each of at least two inverter circuits according to the switching device junction temperature, the preset maximum junction temperature and the total scheduled active current of each of at least two inverter circuits; wherein, for each of the at least two inverter circuits, a square root of a sum of squares of a first reactive current and a first active current of the inverter circuit is less than or equal to a first maximum operating current of the inverter circuit.

13. The system of any one of claims 1 to 12, wherein the controller is any one of the at least two inverter circuits.

14. The system of any one of claims 1 to 13, further comprising at least two dc power sources, each of the at least two dc power sources supplying power to at least one of the inverter circuits.

15. The system according to any one of claims 1 to 14, further comprising at least two filters in one-to-one correspondence with the at least two inverter circuits, the filters being configured to filter the output currents of the inverter circuits.

16. A control method applied to the multiple parallel inverter circuit grid-connected system according to any one of claims 1 to 15, the method comprising:

and controlling the output current of each of the at least two inverter circuits according to the junction temperature of the at least one switching device of each of the at least two inverter circuits, so that the difference between the junction temperature of the at least one switching device of any one of the at least two inverter circuits and the junction temperature of the at least one switching device of any one of the at least two inverter circuits is smaller than or equal to a difference threshold value.

17. The method of claim 16, further comprising:

18. The method of claim 17, wherein the operating parameters comprise at least one of active current, reactive current, apparent current, dc bus voltage, thermal resistivity, switching frequency of switching devices of the inverter circuit, modulated wave, sensed temperature of the inverter circuit.

19. The method according to any one of claims 16 to 18, wherein the controlling the output current of each of the at least two inverter circuits comprises: